The present invention relates to an interface for an in-line liquid chromatograph and mass spectrometer.
When attempting to qualitatively and quantitatively determine the constituents of an unknown substance or substances, oftentimes, the substance is directed to a chromatograph and then either sequentially or subsequently to a mass spectrometer The chromatograph generally separates the nonvolatile components of a substance. The chromatograph, however cannot provide information such as molecular structure, mass of the sample, etc. Thus, it is generally preferred to first direct the sample to the chromatograph and then sequentially direct it to a spectrometer since a spectrometer can provide information about the mass spectra of the substance and therefore greatly facilitate the identification of the components in a substance.
One problem encountered in using such a sequential combination is that liquid chromatography columns and mass spectrometers generally have different pressure and flow requirements. For example, the high flow rates that can be encountered in a liquid chromatograph may inhibit the aerosol ionization required for the mass spectrometer. In addition, attempts to reduce the flow rate of the effluent of the chromatograph and thus, the influent of the mass spectrometer may cause a build-up of pressure greater than that which can be tolerated by the chromatograph.
One solution proposed has been to provide an interface between the chromatograph and the spectrometer. This solution, however, has not been entirely successful.
In addition, another problem exists that has not been addressed by the proposed interface. Mass spectrometers can include an atmospheric pressure chemical ionization probe or an electrospray probe. An atmospheric pressure chemical ionization probe is suitable for volatile components and stable flow is important but not critical for analysis. The electrospray probe is suitable for both volatile and non-volatile components; but stable flow is critical. Thus, it is oftentimes preferred to use both where positively charged ions may be detected in an acidic solution while negatively charged ions may be detected in a basic solution. Consequently, it is desired to modify the mass spectrometer inlet sample by mixing it with an acidic or basic solution to provide the preferred ion detection environment.
There is therefore a need for an interface for an in-line (sequential) chromatograph and mass spectrometer that regulates the inlet flow to the mass spectrometer without creating excessive back pressure and permits addition of a desired ionic solution to the sample being tested. The interface of the present invention accomplishes these desires.